Light is a standard messenger in communications technology. Currently, the bits in data, audio or video traffic are sent through fiber optic cables as brief pulses of light. A pulse is a value of one, and the absence of a pulse equals zero. Each pulse may be millionths of a second or less, and standard fiber optic lines now typically run 2.5 billion to 10 billion bits (2.5 gigabits to 10 gigabits) per second.
The fiber optic cable itself consists of a bundle of single optical fiber strands, each barely the size of a human hair. At the center of each of these strands is the core, made of glass silica. A laser, which encodes data as pulses of light, sends the pulses through the fiber optic cable's core. Surrounding the core is a mirror-like optical material, called the cladding, which reflects the light back into the core. Because the cladding doesn't absorb light, the light pulses are able to travel long distances.
Both transmission lasers and light emitting diodes (LEDs) can be used as the light source, but lasers, which are more powerful, are more commonly employed. The laser can be roughly analogized to an extremely powerful flashlight that blinks billions of time each second. When the laser is turned on, the equivalent of a digital “1” is transmitted, and when it's off, a digital “0” is represented. The high level of internal reflectivity of the cladding in a fiber optic cable allows the light to be transmitted down the length of the cable, even through the many twists and turns of its run.
Light is sent into the fiber, and it bounces back and forth inside the fiber all the way to the other end, which is sometimes hundreds of miles away. Pulses of light in a fiber optic material can carry the same kind of information that is transmitted as electrical pulses in a copper wire. This information can be telephone conversations or data from computers and fax machines. A conventional copper wire can carry a few million electrical pulses each second. In contrast, an optical fiber can carry as many as 20 billion light pulses per second. Telephone companies are switching to fiber optic cables because they can handle huge numbers of conversations at one time, many more than conventional copper wire can carry.